<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<style>
    .lunbo > div {
        width: 50px;
        height: 50px;
        background-color: #d78a32;
        margin: 0 10px;
        float: left;
        margin-top: 200px;
        z-index: 2;
    }

    .lunbo > div:hover .img {
        display: block;
        z-index: -3;
    }

    .img {
        display: none;
        position: absolute;
        top: 0;
        left: 0;
        z-index: -1;
    }

    .lunbo > div:first-child .img {
        display: block;
        z-index: -5;
    }
</style>
<body>
<div class="lunbo">
    <div>
        <div class="img"><img src="../img/21_ttlm.jpg" height="300" width="300"/></div>
    </div>
    <div>
        <div class="img"><img src="../img/46_mkua.jpg" height="300" width="300"/></div>
    </div>
    <div>
        <div class="img"><img src="../img/32_zq2b.jpg" height="300" width="300"/></div>
    </div>
    <div>
        <div class="img"><img src="../img/33_6atw.jpg" height="300" width="300"/></div>
    </div>
</div>
</body>
</html>